2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcExpr]{Typecheck an expression}
7 module TcExpr ( tcExpr, tcExpr_id, tcMonoExpr ) where
9 #include "HsVersions.h"
11 #ifdef GHCI /* Only if bootstrapped */
12 import {-# SOURCE #-} TcSplice( tcSpliceExpr, tcBracket )
13 import HsSyn ( HsReify(..), ReifyFlavour(..) )
14 import TcType ( isTauTy )
15 import TcEnv ( bracketOK, tcMetaTy, checkWellStaged, metaLevel )
16 import TcSimplify ( tcSimplifyBracket )
17 import Name ( isExternalName )
18 import qualified DsMeta
21 import HsSyn ( HsExpr(..), HsLit(..), ArithSeqInfo(..), recBindFields )
22 import RnHsSyn ( RenamedHsExpr, RenamedRecordBinds )
23 import TcHsSyn ( TcExpr, TcRecordBinds, hsLitType, mkHsDictApp, mkHsTyApp, mkHsLet )
25 import TcUnify ( tcSubExp, tcGen, (<$>),
26 unifyTauTy, unifyFunTy, unifyListTy, unifyPArrTy,
28 import BasicTypes ( isMarkedStrict )
29 import Inst ( InstOrigin(..),
30 newOverloadedLit, newMethodFromName, newIPDict,
31 newDicts, newMethodWithGivenTy,
32 instToId, tcInstCall, tcInstDataCon
34 import TcBinds ( tcBindsAndThen )
35 import TcEnv ( tcLookupClass, tcLookupGlobal_maybe, tcLookupIdLvl,
36 tcLookupTyCon, tcLookupDataCon, tcLookupId
38 import TcMatches ( tcMatchesCase, tcMatchLambda, tcDoStmts )
39 import TcMonoType ( tcHsSigType, UserTypeCtxt(..) )
40 import TcPat ( badFieldCon )
41 import TcMType ( tcInstTyVars, tcInstType, newHoleTyVarTy, zapToType,
42 newTyVarTy, newTyVarTys, zonkTcType, readHoleResult )
43 import TcType ( TcType, TcSigmaType, TcRhoType, TyVarDetails(VanillaTv),
44 tcSplitFunTys, tcSplitTyConApp, mkTyVarTys,
45 isSigmaTy, mkFunTy, mkFunTys,
46 mkTyConApp, mkClassPred, tcFunArgTy,
47 tyVarsOfTypes, isLinearPred,
48 liftedTypeKind, openTypeKind,
49 tcSplitSigmaTy, tcTyConAppTyCon,
52 import FieldLabel ( FieldLabel, fieldLabelName, fieldLabelType, fieldLabelTyCon )
53 import Id ( Id, idType, recordSelectorFieldLabel, isRecordSelector )
54 import DataCon ( DataCon, dataConFieldLabels, dataConSig, dataConStrictMarks, dataConWrapId )
56 import TyCon ( TyCon, tyConTyVars, tyConTheta, isAlgTyCon, tyConDataCons, isClassTyCon )
57 import Subst ( mkTopTyVarSubst, substTheta, substTy )
58 import VarSet ( emptyVarSet, elemVarSet )
59 import TysWiredIn ( boolTy )
60 import PrelNames ( cCallableClassName, cReturnableClassName,
61 enumFromName, enumFromThenName,
62 enumFromToName, enumFromThenToName,
63 enumFromToPName, enumFromThenToPName,
66 import ListSetOps ( minusList )
68 import HscTypes ( TyThing(..) )
75 %************************************************************************
77 \subsection{Main wrappers}
79 %************************************************************************
82 tcExpr :: RenamedHsExpr -- Expession to type check
83 -> TcSigmaType -- Expected type (could be a polytpye)
84 -> TcM TcExpr -- Generalised expr with expected type
86 tcExpr expr expected_ty
87 = traceTc (text "tcExpr" <+> (ppr expected_ty $$ ppr expr)) `thenM_`
88 tc_expr' expr expected_ty
90 tc_expr' expr expected_ty
91 | not (isSigmaTy expected_ty) -- Monomorphic case
92 = tcMonoExpr expr expected_ty
95 = tcGen expected_ty emptyVarSet (
97 ) `thenM` \ (gen_fn, expr') ->
98 returnM (gen_fn <$> expr')
102 %************************************************************************
104 \subsection{The TAUT rules for variables}
106 %************************************************************************
109 tcMonoExpr :: RenamedHsExpr -- Expession to type check
110 -> TcRhoType -- Expected type (could be a type variable)
111 -- Definitely no foralls at the top
115 tcMonoExpr (HsVar name) res_ty
116 = tcId name `thenM` \ (expr', id_ty) ->
117 tcSubExp res_ty id_ty `thenM` \ co_fn ->
118 returnM (co_fn <$> expr')
120 tcMonoExpr (HsIPVar ip) res_ty
121 = -- Implicit parameters must have a *tau-type* not a
122 -- type scheme. We enforce this by creating a fresh
123 -- type variable as its type. (Because res_ty may not
125 newTyVarTy openTypeKind `thenM` \ ip_ty ->
126 newIPDict (IPOcc ip) ip ip_ty `thenM` \ (ip', inst) ->
127 extendLIE inst `thenM_`
128 tcSubExp res_ty ip_ty `thenM` \ co_fn ->
129 returnM (co_fn <$> HsIPVar ip')
133 %************************************************************************
135 \subsection{Expressions type signatures}
137 %************************************************************************
140 tcMonoExpr in_expr@(ExprWithTySig expr poly_ty) res_ty
141 = addErrCtxt (exprSigCtxt in_expr) $
142 tcHsSigType ExprSigCtxt poly_ty `thenM` \ sig_tc_ty ->
143 tcExpr expr sig_tc_ty `thenM` \ expr' ->
145 -- Must instantiate the outer for-alls of sig_tc_ty
146 -- else we risk instantiating a ? res_ty to a forall-type
147 -- which breaks the invariant that tcMonoExpr only returns phi-types
148 tcInstCall SignatureOrigin sig_tc_ty `thenM` \ (inst_fn, inst_sig_ty) ->
149 tcSubExp res_ty inst_sig_ty `thenM` \ co_fn ->
151 returnM (co_fn <$> inst_fn expr')
153 tcMonoExpr (HsType ty) res_ty
154 = failWithTc (text "Can't handle type argument:" <+> ppr ty)
155 -- This is the syntax for type applications that I was planning
156 -- but there are difficulties (e.g. what order for type args)
157 -- so it's not enabled yet.
158 -- Can't eliminate it altogether from the parser, because the
159 -- same parser parses *patterns*.
163 %************************************************************************
165 \subsection{Other expression forms}
167 %************************************************************************
170 tcMonoExpr (HsLit lit) res_ty = tcLit lit res_ty
171 tcMonoExpr (HsOverLit lit) res_ty = newOverloadedLit (LiteralOrigin lit) lit res_ty
172 tcMonoExpr (HsPar expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
173 returnM (HsPar expr')
174 tcMonoExpr (HsSCC lbl expr) res_ty = tcMonoExpr expr res_ty `thenM` \ expr' ->
175 returnM (HsSCC lbl expr')
178 tcMonoExpr (NegApp expr neg_name) res_ty
179 = tcMonoExpr (HsApp (HsVar neg_name) expr) res_ty
180 -- ToDo: use tcSyntaxName
182 tcMonoExpr (HsLam match) res_ty
183 = tcMatchLambda match res_ty `thenM` \ match' ->
184 returnM (HsLam match')
186 tcMonoExpr (HsApp e1 e2) res_ty
187 = tcApp e1 [e2] res_ty
190 Note that the operators in sections are expected to be binary, and
191 a type error will occur if they aren't.
194 -- Left sections, equivalent to
201 tcMonoExpr in_expr@(SectionL arg1 op) res_ty
202 = tcExpr_id op `thenM` \ (op', op_ty) ->
203 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
204 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
205 addErrCtxt (exprCtxt in_expr) $
206 tcSubExp res_ty (mkFunTy arg2_ty op_res_ty) `thenM` \ co_fn ->
207 returnM (co_fn <$> SectionL arg1' op')
209 -- Right sections, equivalent to \ x -> x op expr, or
212 tcMonoExpr in_expr@(SectionR op arg2) res_ty
213 = tcExpr_id op `thenM` \ (op', op_ty) ->
214 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
215 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
216 addErrCtxt (exprCtxt in_expr) $
217 tcSubExp res_ty (mkFunTy arg1_ty op_res_ty) `thenM` \ co_fn ->
218 returnM (co_fn <$> SectionR op' arg2')
220 -- equivalent to (op e1) e2:
222 tcMonoExpr in_expr@(OpApp arg1 op fix arg2) res_ty
223 = tcExpr_id op `thenM` \ (op', op_ty) ->
224 split_fun_ty op_ty 2 {- two args -} `thenM` \ ([arg1_ty, arg2_ty], op_res_ty) ->
225 tcArg op (arg1, arg1_ty, 1) `thenM` \ arg1' ->
226 tcArg op (arg2, arg2_ty, 2) `thenM` \ arg2' ->
227 addErrCtxt (exprCtxt in_expr) $
228 tcSubExp res_ty op_res_ty `thenM` \ co_fn ->
229 returnM (OpApp arg1' op' fix arg2')
233 tcMonoExpr (HsLet binds expr) res_ty
236 binds -- Bindings to check
237 (tcMonoExpr expr res_ty)
239 tcMonoExpr in_expr@(HsCase scrut matches src_loc) res_ty
240 = addSrcLoc src_loc $
241 addErrCtxt (caseCtxt in_expr) $
243 -- Typecheck the case alternatives first.
244 -- The case patterns tend to give good type info to use
245 -- when typechecking the scrutinee. For example
248 -- will report that map is applied to too few arguments
250 -- Not only that, but it's better to check the matches on their
251 -- own, so that we get the expected results for scoped type variables.
253 -- (p::a, q::b) -> (q,p)
254 -- The above should work: the match (p,q) -> (q,p) is polymorphic as
255 -- claimed by the pattern signatures. But if we typechecked the
256 -- match with x in scope and x's type as the expected type, we'd be hosed.
258 tcMatchesCase matches res_ty `thenM` \ (scrut_ty, matches') ->
260 addErrCtxt (caseScrutCtxt scrut) (
261 tcMonoExpr scrut scrut_ty
262 ) `thenM` \ scrut' ->
264 returnM (HsCase scrut' matches' src_loc)
266 tcMonoExpr (HsIf pred b1 b2 src_loc) res_ty
267 = addSrcLoc src_loc $
268 addErrCtxt (predCtxt pred) (
269 tcMonoExpr pred boolTy ) `thenM` \ pred' ->
271 zapToType res_ty `thenM` \ res_ty' ->
272 -- C.f. the call to zapToType in TcMatches.tcMatches
274 tcMonoExpr b1 res_ty' `thenM` \ b1' ->
275 tcMonoExpr b2 res_ty' `thenM` \ b2' ->
276 returnM (HsIf pred' b1' b2' src_loc)
278 tcMonoExpr (HsDo do_or_lc stmts method_names _ src_loc) res_ty
279 = addSrcLoc src_loc $
280 tcDoStmts do_or_lc stmts method_names res_ty `thenM` \ (binds, stmts', methods') ->
281 returnM (mkHsLet binds (HsDo do_or_lc stmts' methods' res_ty src_loc))
283 tcMonoExpr in_expr@(ExplicitList _ exprs) res_ty -- Non-empty list
284 = unifyListTy res_ty `thenM` \ elt_ty ->
285 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
286 returnM (ExplicitList elt_ty exprs')
289 = addErrCtxt (listCtxt expr) $
290 tcMonoExpr expr elt_ty
292 tcMonoExpr in_expr@(ExplicitPArr _ exprs) res_ty -- maybe empty
293 = unifyPArrTy res_ty `thenM` \ elt_ty ->
294 mappM (tc_elt elt_ty) exprs `thenM` \ exprs' ->
295 returnM (ExplicitPArr elt_ty exprs')
298 = addErrCtxt (parrCtxt expr) $
299 tcMonoExpr expr elt_ty
301 tcMonoExpr (ExplicitTuple exprs boxity) res_ty
302 = unifyTupleTy boxity (length exprs) res_ty `thenM` \ arg_tys ->
303 tcMonoExprs exprs arg_tys `thenM` \ exprs' ->
304 returnM (ExplicitTuple exprs' boxity)
308 %************************************************************************
312 %************************************************************************
314 The interesting thing about @ccall@ is that it is just a template
315 which we instantiate by filling in details about the types of its
316 argument and result (ie minimal typechecking is performed). So, the
317 basic story is that we allocate a load of type variables (to hold the
318 arg/result types); unify them with the args/result; and store them for
322 tcMonoExpr e0@(HsCCall lbl args may_gc is_casm ignored_fake_result_ty) res_ty
324 = getDOpts `thenM` \ dflags ->
326 checkTc (not (is_casm && dopt_HscLang dflags /= HscC))
327 (vcat [text "_casm_ is only supported when compiling via C (-fvia-C).",
328 text "Either compile with -fvia-C, or, better, rewrite your code",
329 text "to use the foreign function interface. _casm_s are deprecated",
330 text "and support for them may one day disappear."])
333 -- Get the callable and returnable classes.
334 tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
335 tcLookupClass cReturnableClassName `thenM` \ cReturnableClass ->
336 tcLookupTyCon ioTyConName `thenM` \ ioTyCon ->
338 new_arg_dict (arg, arg_ty)
339 = newDicts (CCallOrigin (unpackFS lbl) (Just arg))
340 [mkClassPred cCallableClass [arg_ty]] `thenM` \ arg_dicts ->
341 returnM arg_dicts -- Actually a singleton bag
343 result_origin = CCallOrigin (unpackFS lbl) Nothing {- Not an arg -}
347 let tv_idxs | null args = []
348 | otherwise = [1..length args]
350 newTyVarTys (length tv_idxs) openTypeKind `thenM` \ arg_tys ->
351 tcMonoExprs args arg_tys `thenM` \ args' ->
353 -- The argument types can be unlifted or lifted; the result
354 -- type must, however, be lifted since it's an argument to the IO
356 newTyVarTy liftedTypeKind `thenM` \ result_ty ->
358 io_result_ty = mkTyConApp ioTyCon [result_ty]
360 unifyTauTy res_ty io_result_ty `thenM_`
362 -- Construct the extra insts, which encode the
363 -- constraints on the argument and result types.
364 mappM new_arg_dict (zipEqual "tcMonoExpr:CCall" args arg_tys) `thenM` \ ccarg_dicts_s ->
365 newDicts result_origin [mkClassPred cReturnableClass [result_ty]] `thenM` \ ccres_dict ->
366 extendLIEs (ccres_dict ++ concat ccarg_dicts_s) `thenM_`
367 returnM (HsCCall lbl args' may_gc is_casm io_result_ty)
371 %************************************************************************
373 Record construction and update
375 %************************************************************************
378 tcMonoExpr expr@(RecordCon con_name rbinds) res_ty
379 = addErrCtxt (recordConCtxt expr) $
380 tcId con_name `thenM` \ (con_expr, con_tau) ->
382 (_, record_ty) = tcSplitFunTys con_tau
383 (tycon, ty_args) = tcSplitTyConApp record_ty
385 ASSERT( isAlgTyCon tycon )
386 unifyTauTy res_ty record_ty `thenM_`
388 -- Check that the record bindings match the constructor
389 -- con_name is syntactically constrained to be a data constructor
390 tcLookupDataCon con_name `thenM` \ data_con ->
392 bad_fields = badFields rbinds data_con
394 if notNull bad_fields then
395 mappM (addErrTc . badFieldCon data_con) bad_fields `thenM_`
396 failM -- Fail now, because tcRecordBinds will crash on a bad field
399 -- Typecheck the record bindings
400 tcRecordBinds tycon ty_args rbinds `thenM` \ rbinds' ->
402 -- Check for missing fields
403 checkMissingFields data_con rbinds `thenM_`
405 returnM (RecordConOut data_con con_expr rbinds')
407 -- The main complication with RecordUpd is that we need to explicitly
408 -- handle the *non-updated* fields. Consider:
410 -- data T a b = MkT1 { fa :: a, fb :: b }
411 -- | MkT2 { fa :: a, fc :: Int -> Int }
412 -- | MkT3 { fd :: a }
414 -- upd :: T a b -> c -> T a c
415 -- upd t x = t { fb = x}
417 -- The type signature on upd is correct (i.e. the result should not be (T a b))
418 -- because upd should be equivalent to:
420 -- upd t x = case t of
421 -- MkT1 p q -> MkT1 p x
422 -- MkT2 a b -> MkT2 p b
423 -- MkT3 d -> error ...
425 -- So we need to give a completely fresh type to the result record,
426 -- and then constrain it by the fields that are *not* updated ("p" above).
428 -- Note that because MkT3 doesn't contain all the fields being updated,
429 -- its RHS is simply an error, so it doesn't impose any type constraints
431 -- All this is done in STEP 4 below.
433 tcMonoExpr expr@(RecordUpd record_expr rbinds) res_ty
434 = addErrCtxt (recordUpdCtxt expr) $
437 -- Check that the field names are really field names
438 ASSERT( notNull rbinds )
440 field_names = recBindFields rbinds
442 mappM tcLookupGlobal_maybe field_names `thenM` \ maybe_sel_ids ->
444 bad_guys = [ addErrTc (notSelector field_name)
445 | (field_name, maybe_sel_id) <- field_names `zip` maybe_sel_ids,
446 not (is_selector maybe_sel_id)
448 is_selector (Just (AnId sel_id))
449 = isRecordSelector sel_id && -- At the moment, class ops are
450 -- treated as record selectors, but
451 -- we want to exclude that case here
452 not (isClassTyCon (fieldLabelTyCon (recordSelectorFieldLabel sel_id)))
453 is_selector other = False
455 checkM (null bad_guys) (sequenceM bad_guys `thenM_` failM) `thenM_`
458 -- Figure out the tycon and data cons from the first field name
460 -- It's OK to use the non-tc splitters here (for a selector)
461 (Just (AnId sel_id) : _) = maybe_sel_ids
462 field_lbl = recordSelectorFieldLabel sel_id -- We've failed already if
463 tycon = fieldLabelTyCon field_lbl -- it's not a field label
464 data_cons = tyConDataCons tycon
465 tycon_tyvars = tyConTyVars tycon -- The data cons use the same type vars
467 tcInstTyVars VanillaTv tycon_tyvars `thenM` \ (_, result_inst_tys, inst_env) ->
470 -- Check that at least one constructor has all the named fields
471 -- i.e. has an empty set of bad fields returned by badFields
472 checkTc (any (null . badFields rbinds) data_cons)
473 (badFieldsUpd rbinds) `thenM_`
476 -- Typecheck the update bindings.
477 -- (Do this after checking for bad fields in case there's a field that
478 -- doesn't match the constructor.)
480 result_record_ty = mkTyConApp tycon result_inst_tys
482 unifyTauTy res_ty result_record_ty `thenM_`
483 tcRecordBinds tycon result_inst_tys rbinds `thenM` \ rbinds' ->
486 -- Use the un-updated fields to find a vector of booleans saying
487 -- which type arguments must be the same in updatee and result.
489 -- WARNING: this code assumes that all data_cons in a common tycon
490 -- have FieldLabels abstracted over the same tyvars.
492 upd_field_lbls = map recordSelectorFieldLabel (recBindFields rbinds')
493 con_field_lbls_s = map dataConFieldLabels data_cons
495 -- A constructor is only relevant to this process if
496 -- it contains all the fields that are being updated
497 relevant_field_lbls_s = filter is_relevant con_field_lbls_s
498 is_relevant con_field_lbls = all (`elem` con_field_lbls) upd_field_lbls
500 non_upd_field_lbls = concat relevant_field_lbls_s `minusList` upd_field_lbls
501 common_tyvars = tyVarsOfTypes (map fieldLabelType non_upd_field_lbls)
503 mk_inst_ty (tyvar, result_inst_ty)
504 | tyvar `elemVarSet` common_tyvars = returnM result_inst_ty -- Same as result type
505 | otherwise = newTyVarTy liftedTypeKind -- Fresh type
507 mappM mk_inst_ty (zip tycon_tyvars result_inst_tys) `thenM` \ inst_tys ->
510 -- Typecheck the expression to be updated
512 record_ty = mkTyConApp tycon inst_tys
514 tcMonoExpr record_expr record_ty `thenM` \ record_expr' ->
517 -- Figure out the LIE we need. We have to generate some
518 -- dictionaries for the data type context, since we are going to
519 -- do pattern matching over the data cons.
521 -- What dictionaries do we need?
522 -- We just take the context of the type constructor
524 theta' = substTheta inst_env (tyConTheta tycon)
526 newDicts RecordUpdOrigin theta' `thenM` \ dicts ->
527 extendLIEs dicts `thenM_`
530 returnM (RecordUpdOut record_expr' record_ty result_record_ty rbinds')
534 %************************************************************************
536 Arithmetic sequences e.g. [a,b..]
537 and their parallel-array counterparts e.g. [: a,b.. :]
540 %************************************************************************
543 tcMonoExpr (ArithSeqIn seq@(From expr)) res_ty
544 = unifyListTy res_ty `thenM` \ elt_ty ->
545 tcMonoExpr expr elt_ty `thenM` \ expr' ->
547 newMethodFromName (ArithSeqOrigin seq)
548 elt_ty enumFromName `thenM` \ enum_from ->
550 returnM (ArithSeqOut (HsVar enum_from) (From expr'))
552 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThen expr1 expr2)) res_ty
553 = addErrCtxt (arithSeqCtxt in_expr) $
554 unifyListTy res_ty `thenM` \ elt_ty ->
555 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
556 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
557 newMethodFromName (ArithSeqOrigin seq)
558 elt_ty enumFromThenName `thenM` \ enum_from_then ->
560 returnM (ArithSeqOut (HsVar enum_from_then) (FromThen expr1' expr2'))
563 tcMonoExpr in_expr@(ArithSeqIn seq@(FromTo expr1 expr2)) res_ty
564 = addErrCtxt (arithSeqCtxt in_expr) $
565 unifyListTy res_ty `thenM` \ elt_ty ->
566 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
567 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
568 newMethodFromName (ArithSeqOrigin seq)
569 elt_ty enumFromToName `thenM` \ enum_from_to ->
571 returnM (ArithSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
573 tcMonoExpr in_expr@(ArithSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
574 = addErrCtxt (arithSeqCtxt in_expr) $
575 unifyListTy res_ty `thenM` \ elt_ty ->
576 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
577 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
578 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
579 newMethodFromName (ArithSeqOrigin seq)
580 elt_ty enumFromThenToName `thenM` \ eft ->
582 returnM (ArithSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
584 tcMonoExpr in_expr@(PArrSeqIn seq@(FromTo expr1 expr2)) res_ty
585 = addErrCtxt (parrSeqCtxt in_expr) $
586 unifyPArrTy res_ty `thenM` \ elt_ty ->
587 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
588 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
589 newMethodFromName (PArrSeqOrigin seq)
590 elt_ty enumFromToPName `thenM` \ enum_from_to ->
592 returnM (PArrSeqOut (HsVar enum_from_to) (FromTo expr1' expr2'))
594 tcMonoExpr in_expr@(PArrSeqIn seq@(FromThenTo expr1 expr2 expr3)) res_ty
595 = addErrCtxt (parrSeqCtxt in_expr) $
596 unifyPArrTy res_ty `thenM` \ elt_ty ->
597 tcMonoExpr expr1 elt_ty `thenM` \ expr1' ->
598 tcMonoExpr expr2 elt_ty `thenM` \ expr2' ->
599 tcMonoExpr expr3 elt_ty `thenM` \ expr3' ->
600 newMethodFromName (PArrSeqOrigin seq)
601 elt_ty enumFromThenToPName `thenM` \ eft ->
603 returnM (PArrSeqOut (HsVar eft) (FromThenTo expr1' expr2' expr3'))
605 tcMonoExpr (PArrSeqIn _) _
606 = panic "TcExpr.tcMonoExpr: Infinite parallel array!"
607 -- the parser shouldn't have generated it and the renamer shouldn't have
612 %************************************************************************
616 %************************************************************************
619 #ifdef GHCI /* Only if bootstrapped */
620 -- Rename excludes these cases otherwise
622 tcMonoExpr (HsSplice n expr loc) res_ty = addSrcLoc loc (tcSpliceExpr n expr res_ty)
624 tcMonoExpr (HsBracket brack loc) res_ty
626 getStage `thenM` \ level ->
627 case bracketOK level of {
628 Nothing -> failWithTc (illegalBracket level) ;
631 -- Typecheck expr to make sure it is valid,
632 -- but throw away the results. We'll type check
633 -- it again when we actually use it.
634 newMutVar [] `thenM` \ pending_splices ->
635 getLIEVar `thenM` \ lie_var ->
637 setStage (Brack next_level pending_splices lie_var) (
638 getLIE (tcBracket brack)
639 ) `thenM` \ (meta_ty, lie) ->
640 tcSimplifyBracket lie `thenM_`
642 unifyTauTy res_ty meta_ty `thenM_`
644 -- Return the original expression, not the type-decorated one
645 readMutVar pending_splices `thenM` \ pendings ->
646 returnM (HsBracketOut brack pendings)
649 tcMonoExpr (HsReify (Reify flavour name)) res_ty
650 = addErrCtxt (ptext SLIT("At the reification of") <+> ppr name) $
651 tcMetaTy tycon_name `thenM` \ reify_ty ->
652 unifyTauTy res_ty reify_ty `thenM_`
653 returnM (HsReify (ReifyOut flavour name))
655 tycon_name = case flavour of
656 ReifyDecl -> DsMeta.declTyConName
657 ReifyType -> DsMeta.typeTyConName
658 ReifyFixity -> pprPanic "tcMonoExpr: cant do reifyFixity yet" (ppr name)
663 %************************************************************************
667 %************************************************************************
670 tcMonoExpr other _ = pprPanic "tcMonoExpr" (ppr other)
674 %************************************************************************
676 \subsection{@tcApp@ typchecks an application}
678 %************************************************************************
682 tcApp :: RenamedHsExpr -> [RenamedHsExpr] -- Function and args
683 -> TcType -- Expected result type of application
684 -> TcM TcExpr -- Translated fun and args
686 tcApp (HsApp e1 e2) args res_ty
687 = tcApp e1 (e2:args) res_ty -- Accumulate the arguments
689 tcApp fun args res_ty
690 = -- First type-check the function
691 tcExpr_id fun `thenM` \ (fun', fun_ty) ->
693 addErrCtxt (wrongArgsCtxt "too many" fun args) (
694 traceTc (text "tcApp" <+> (ppr fun $$ ppr fun_ty)) `thenM_`
695 split_fun_ty fun_ty (length args)
696 ) `thenM` \ (expected_arg_tys, actual_result_ty) ->
698 -- Now typecheck the args
700 (zip3 args expected_arg_tys [1..]) `thenM` \ args' ->
702 -- Unify with expected result after type-checking the args
703 -- so that the info from args percolates to actual_result_ty.
704 -- This is when we might detect a too-few args situation.
705 -- (One can think of cases when the opposite order would give
706 -- a better error message.)
707 addErrCtxtM (checkArgsCtxt fun args res_ty actual_result_ty)
708 (tcSubExp res_ty actual_result_ty) `thenM` \ co_fn ->
710 returnM (co_fn <$> foldl HsApp fun' args')
713 -- If an error happens we try to figure out whether the
714 -- function has been given too many or too few arguments,
716 checkArgsCtxt fun args expected_res_ty actual_res_ty tidy_env
717 = zonkTcType expected_res_ty `thenM` \ exp_ty' ->
718 zonkTcType actual_res_ty `thenM` \ act_ty' ->
720 (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
721 (env2, act_ty'') = tidyOpenType env1 act_ty'
722 (exp_args, _) = tcSplitFunTys exp_ty''
723 (act_args, _) = tcSplitFunTys act_ty''
725 len_act_args = length act_args
726 len_exp_args = length exp_args
728 message | len_exp_args < len_act_args = wrongArgsCtxt "too few" fun args
729 | len_exp_args > len_act_args = wrongArgsCtxt "too many" fun args
730 | otherwise = appCtxt fun args
732 returnM (env2, message)
735 split_fun_ty :: TcType -- The type of the function
736 -> Int -- Number of arguments
737 -> TcM ([TcType], -- Function argument types
738 TcType) -- Function result types
740 split_fun_ty fun_ty 0
741 = returnM ([], fun_ty)
743 split_fun_ty fun_ty n
744 = -- Expect the function to have type A->B
745 unifyFunTy fun_ty `thenM` \ (arg_ty, res_ty) ->
746 split_fun_ty res_ty (n-1) `thenM` \ (arg_tys, final_res_ty) ->
747 returnM (arg_ty:arg_tys, final_res_ty)
751 tcArg :: RenamedHsExpr -- The function (for error messages)
752 -> (RenamedHsExpr, TcSigmaType, Int) -- Actual argument and expected arg type
753 -> TcM TcExpr -- Resulting argument and LIE
755 tcArg the_fun (arg, expected_arg_ty, arg_no)
756 = addErrCtxt (funAppCtxt the_fun arg arg_no) $
757 tcExpr arg expected_arg_ty
761 %************************************************************************
763 \subsection{@tcId@ typchecks an identifier occurrence}
765 %************************************************************************
767 tcId instantiates an occurrence of an Id.
768 The instantiate_it loop runs round instantiating the Id.
769 It has to be a loop because we are now prepared to entertain
771 f:: forall a. Eq a => forall b. Baz b => tau
772 We want to instantiate this to
773 f2::tau {f2 = f1 b (Baz b), f1 = f a (Eq a)}
775 The -fno-method-sharing flag controls what happens so far as the LIE
776 is concerned. The default case is that for an overloaded function we
777 generate a "method" Id, and add the Method Inst to the LIE. So you get
780 f = /\a (d:Num a) -> let m = (+) a d in \ (x:a) -> m x x
781 If you specify -fno-method-sharing, the dictionary application
782 isn't shared, so we get
784 f = /\a (d:Num a) (x:a) -> (+) a d x x
785 This gets a bit less sharing, but
786 a) it's better for RULEs involving overloaded functions
787 b) perhaps fewer separated lambdas
790 tcId :: Name -> TcM (TcExpr, TcType)
791 tcId name -- Look up the Id and instantiate its type
792 = -- First check whether it's a DataCon
793 -- Reason: we must not forget to chuck in the
794 -- constraints from their "silly context"
795 tcLookupGlobal_maybe name `thenM` \ maybe_thing ->
796 case maybe_thing of {
797 Just (ADataCon data_con) -> inst_data_con data_con ;
800 -- OK, so now look for ordinary Ids
801 tcLookupIdLvl name `thenM` \ (id, bind_lvl) ->
804 loop (HsVar id) (idType id) -- Non-TH case
806 #else /* GHCI is on */
807 -- Check for cross-stage lifting
808 getStage `thenM` \ use_stage ->
810 Brack use_lvl ps_var lie_var
811 | use_lvl > bind_lvl && not (isExternalName name)
812 -> -- E.g. \x -> [| h x |]
813 -- We must behave as if the reference to x was
815 -- We use 'x' itself as the splice proxy, used by
816 -- the desugarer to stitch it all back together.
817 -- If 'x' occurs many times we may get many identical
818 -- bindings of the same splice proxy, but that doesn't
819 -- matter, although it's a mite untidy.
821 -- NB: During type-checking, isExernalName is true of
822 -- top level things, and false of nested bindings
823 -- Top-level things don't need lifting.
828 checkTc (isTauTy id_ty) (polySpliceErr id) `thenM_`
829 -- If x is polymorphic, its occurrence sites might
830 -- have different instantiations, so we can't use plain
831 -- 'x' as the splice proxy name. I don't know how to
832 -- solve this, and it's probably unimportant, so I'm
833 -- just going to flag an error for now
836 newMethodFromName orig id_ty DsMeta.liftName `thenM` \ lift ->
837 -- Put the 'lift' constraint into the right LIE
839 -- Update the pending splices
840 readMutVar ps_var `thenM` \ ps ->
841 writeMutVar ps_var ((name, HsApp (HsVar lift) (HsVar id)) : ps) `thenM_`
843 returnM (HsVar id, id_ty))
846 checkWellStaged (quotes (ppr id)) bind_lvl use_stage `thenM_`
847 loop (HsVar id) (idType id)
852 orig = OccurrenceOf name
854 loop (HsVar fun_id) fun_ty
855 | want_method_inst fun_ty
856 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
857 newMethodWithGivenTy orig fun_id
858 (mkTyVarTys tyvars) theta tau `thenM` \ meth_id ->
859 loop (HsVar meth_id) tau
863 = tcInstCall orig fun_ty `thenM` \ (inst_fn, tau) ->
864 loop (inst_fn fun) tau
867 = returnM (fun, fun_ty)
869 -- Hack Alert (want_method_inst)!
870 -- If f :: (%x :: T) => Int -> Int
871 -- Then if we have two separate calls, (f 3, f 4), we cannot
872 -- make a method constraint that then gets shared, thus:
873 -- let m = f %x in (m 3, m 4)
874 -- because that loses the linearity of the constraint.
875 -- The simplest thing to do is never to construct a method constraint
876 -- in the first place that has a linear implicit parameter in it.
877 want_method_inst fun_ty
878 | opt_NoMethodSharing = False
879 | otherwise = case tcSplitSigmaTy fun_ty of
880 (_,[],_) -> False -- Not overloaded
881 (_,theta,_) -> not (any isLinearPred theta)
884 -- We treat data constructors differently, because we have to generate
885 -- constraints for their silly theta, which no longer appears in
886 -- the type of dataConWrapId. It's dual to TcPat.tcConstructor
887 inst_data_con data_con
888 = tcInstDataCon orig data_con `thenM` \ (ty_args, ex_dicts, arg_tys, result_ty, _) ->
889 extendLIEs ex_dicts `thenM_`
890 returnM (mkHsDictApp (mkHsTyApp (HsVar (dataConWrapId data_con)) ty_args)
891 (map instToId ex_dicts),
892 mkFunTys arg_tys result_ty)
895 Typecheck expression which in most cases will be an Id.
896 The expression can return a higher-ranked type, such as
897 (forall a. a->a) -> Int
898 so we must create a HoleTyVarTy to pass in as the expected tyvar.
901 tcExpr_id :: RenamedHsExpr -> TcM (TcExpr, TcType)
902 tcExpr_id (HsVar name) = tcId name
903 tcExpr_id expr = newHoleTyVarTy `thenM` \ id_ty ->
904 tcMonoExpr expr id_ty `thenM` \ expr' ->
905 readHoleResult id_ty `thenM` \ id_ty' ->
906 returnM (expr', id_ty')
910 %************************************************************************
912 \subsection{Record bindings}
914 %************************************************************************
916 Game plan for record bindings
917 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
918 1. Find the TyCon for the bindings, from the first field label.
920 2. Instantiate its tyvars and unify (T a1 .. an) with expected_ty.
922 For each binding field = value
924 3. Instantiate the field type (from the field label) using the type
927 4 Type check the value using tcArg, passing the field type as
928 the expected argument type.
930 This extends OK when the field types are universally quantified.
935 :: TyCon -- Type constructor for the record
936 -> [TcType] -- Args of this type constructor
937 -> RenamedRecordBinds
940 tcRecordBinds tycon ty_args rbinds
941 = mappM do_bind rbinds
943 tenv = mkTopTyVarSubst (tyConTyVars tycon) ty_args
945 do_bind (field_lbl_name, rhs)
946 = addErrCtxt (fieldCtxt field_lbl_name) $
947 tcLookupId field_lbl_name `thenM` \ sel_id ->
949 field_lbl = recordSelectorFieldLabel sel_id
950 field_ty = substTy tenv (fieldLabelType field_lbl)
952 ASSERT( isRecordSelector sel_id )
953 -- This lookup and assertion will surely succeed, because
954 -- we check that the fields are indeed record selectors
955 -- before calling tcRecordBinds
956 ASSERT2( fieldLabelTyCon field_lbl == tycon, ppr field_lbl )
957 -- The caller of tcRecordBinds has already checked
958 -- that all the fields come from the same type
960 tcExpr rhs field_ty `thenM` \ rhs' ->
962 returnM (sel_id, rhs')
964 badFields rbinds data_con
965 = filter (not . (`elem` field_names)) (recBindFields rbinds)
967 field_names = map fieldLabelName (dataConFieldLabels data_con)
969 checkMissingFields :: DataCon -> RenamedRecordBinds -> TcM ()
970 checkMissingFields data_con rbinds
971 | null field_labels -- Not declared as a record;
972 -- But C{} is still valid if no strict fields
973 = if any isMarkedStrict field_strs then
974 -- Illegal if any arg is strict
975 addErrTc (missingStrictFields data_con [])
979 | otherwise -- A record
980 = checkM (null missing_s_fields)
981 (addErrTc (missingStrictFields data_con missing_s_fields)) `thenM_`
983 doptM Opt_WarnMissingFields `thenM` \ warn ->
984 checkM (not (warn && notNull missing_ns_fields))
985 (warnTc True (missingFields data_con missing_ns_fields))
989 = [ fl | (fl, str) <- field_info,
991 not (fieldLabelName fl `elem` field_names_used)
994 = [ fl | (fl, str) <- field_info,
995 not (isMarkedStrict str),
996 not (fieldLabelName fl `elem` field_names_used)
999 field_names_used = recBindFields rbinds
1000 field_labels = dataConFieldLabels data_con
1002 field_info = zipEqual "missingFields"
1006 field_strs = dropList ex_theta (dataConStrictMarks data_con)
1007 -- The 'drop' is because dataConStrictMarks
1008 -- includes the existential dictionaries
1009 (_, _, _, ex_theta, _, _) = dataConSig data_con
1012 %************************************************************************
1014 \subsection{@tcMonoExprs@ typechecks a {\em list} of expressions}
1016 %************************************************************************
1019 tcMonoExprs :: [RenamedHsExpr] -> [TcType] -> TcM [TcExpr]
1021 tcMonoExprs [] [] = returnM []
1022 tcMonoExprs (expr:exprs) (ty:tys)
1023 = tcMonoExpr expr ty `thenM` \ expr' ->
1024 tcMonoExprs exprs tys `thenM` \ exprs' ->
1025 returnM (expr':exprs')
1029 %************************************************************************
1031 \subsection{Literals}
1033 %************************************************************************
1035 Overloaded literals.
1038 tcLit :: HsLit -> TcType -> TcM TcExpr
1039 tcLit (HsLitLit s _) res_ty
1040 = tcLookupClass cCallableClassName `thenM` \ cCallableClass ->
1041 newDicts (LitLitOrigin (unpackFS s))
1042 [mkClassPred cCallableClass [res_ty]] `thenM` \ dicts ->
1043 extendLIEs dicts `thenM_`
1044 returnM (HsLit (HsLitLit s res_ty))
1047 = unifyTauTy res_ty (hsLitType lit) `thenM_`
1052 %************************************************************************
1054 \subsection{Errors and contexts}
1056 %************************************************************************
1058 Boring and alphabetical:
1061 = hang (ptext SLIT("In an arithmetic sequence:")) 4 (ppr expr)
1064 = hang (ptext SLIT("In a parallel array sequence:")) 4 (ppr expr)
1067 = hang (ptext SLIT("In the case expression:")) 4 (ppr expr)
1070 = hang (ptext SLIT("In the scrutinee of a case expression:")) 4 (ppr expr)
1073 = hang (ptext SLIT("When checking the type signature of the expression:"))
1077 = hang (ptext SLIT("In the expression:")) 4 (ppr expr)
1079 fieldCtxt field_name
1080 = ptext SLIT("In the") <+> quotes (ppr field_name) <+> ptext SLIT("field of a record")
1082 funAppCtxt fun arg arg_no
1083 = hang (hsep [ ptext SLIT("In the"), speakNth arg_no, ptext SLIT("argument of"),
1084 quotes (ppr fun) <> text ", namely"])
1085 4 (quotes (ppr arg))
1088 = hang (ptext SLIT("In the list element:")) 4 (ppr expr)
1091 = hang (ptext SLIT("In the parallel array element:")) 4 (ppr expr)
1094 = hang (ptext SLIT("In the predicate expression:")) 4 (ppr expr)
1096 illegalBracket level
1097 = ptext SLIT("Illegal bracket at level") <+> ppr level
1100 = ptext SLIT("In the application") <+> quotes (ppr the_app)
1102 the_app = foldl HsApp fun args -- Used in error messages
1104 lurkingRank2Err fun fun_ty
1105 = hang (hsep [ptext SLIT("Illegal use of"), quotes (ppr fun)])
1106 4 (vcat [ptext SLIT("It is applied to too few arguments"),
1107 ptext SLIT("so that the result type has for-alls in it:") <+> ppr fun_ty])
1110 = hang (ptext SLIT("No constructor has all these fields:"))
1111 4 (pprQuotedList (recBindFields rbinds))
1113 recordUpdCtxt expr = ptext SLIT("In the record update:") <+> ppr expr
1114 recordConCtxt expr = ptext SLIT("In the record construction:") <+> ppr expr
1117 = hsep [quotes (ppr field), ptext SLIT("is not a record selector")]
1119 missingStrictFields :: DataCon -> [FieldLabel] -> SDoc
1120 missingStrictFields con fields
1123 rest | null fields = empty -- Happens for non-record constructors
1124 -- with strict fields
1125 | otherwise = colon <+> pprWithCommas ppr fields
1127 header = ptext SLIT("Constructor") <+> quotes (ppr con) <+>
1128 ptext SLIT("does not have the required strict field(s)")
1130 missingFields :: DataCon -> [FieldLabel] -> SDoc
1131 missingFields con fields
1132 = ptext SLIT("Fields of") <+> quotes (ppr con) <+> ptext SLIT("not initialised:")
1133 <+> pprWithCommas ppr fields
1135 polySpliceErr :: Id -> SDoc
1137 = ptext SLIT("Can't splice the polymorphic local variable") <+> quotes (ppr id)
1139 wrongArgsCtxt too_many_or_few fun args
1140 = hang (ptext SLIT("Probable cause:") <+> quotes (ppr fun)
1141 <+> ptext SLIT("is applied to") <+> text too_many_or_few
1142 <+> ptext SLIT("arguments in the call"))
1143 4 (parens (ppr the_app))
1145 the_app = foldl HsApp fun args -- Used in error messages